Variable ND Filters and Metering problems

I have bought a variable ND filter (admittedly a cheap one to try out before flashing the cash for an expensive one!), and I find that the cameras metering begins to under-expose significantly above about +4 to +5 stops. I'm using a K-r and for my test used centre weighted metering and aperture priority, before I switched switch to manual.

At small adjustments there was not much colour cast and that could be sorted in processing, but a high levels (+7 or more) quite a strong colour cast and other distortions making it not realistically usable, but I realise that you get what you pay for, so I shouldn't expect miracles.

Any thoughts/suggestions on the metering issue and recommendations for an affordable (less that £75) variable ND filter 62mm thread?

I have a 62mm variable ND filter from 7 Day Shop. I suspect you might have the same one, though. I haven't noticed the under-exposure problems, though I have noticed a bit of a colour cast at the darker settings as you have. I haven't really noticed any distortions, but haven't used that much either so perhaps haven't had the subjects to do this.

I think you will always find problems with a one size fits all filter compared with specialist ones costing a lot more. I doubt any variable ND filter at under £75 will be any better. I expected limitations when I bought it and, to be honest, it's been better than I thought. I just wanted to see if I used it enough to justify buying the better filters and, so far, I haven't been tempted.

Using a K-r as well.

I also have the 7 day shop variable ND filters and have had good results with them. You do lose a little sharpness, but the only colour cast I have noticed is a slight warming effect which helps to bring the colours out. The best advice I can give is not to turn the filters too far to the max, otherwise the images will have dark blotches on them. Regarding exposure, I think you should always shoot in manual mode whenever you use any ND filter that cuts out a lot of light, whether it's cheap or expensive. All DSLR's will have a tendency to underexpose when there is very little light and the darker it gets the more this will happen.

Spend £100 or more and you will get better ND filters, but for the price I have no complaints about the 7 Day Shop ones and I have used them quite a lot.

Regards
David

David & Milamder
Thanks for your comments and advice. David - I'm sure that you're right about always shooting in manual - advice I intend to follow.

Are you covering the viewfinder? Light gets in there which would result in underexposure

I've just sent back the 77mm version from 7Dayshop. I have the 62mm version and had slightly more success with that. It could well have been me and not the filter 77mm ND Tamron 10-24mm on K5. Help

#1
[IMG]http://i1100.photobucket.com/albums/g406/tyronet2000/Cresswell%20ND/resize_K5_1576.jpg[/IMG]

#2
[IMG]http://i1100.photobucket.com/albums/g406/tyronet2000/Cresswell%20ND/resize_K5_1577.jpg[/IMG]

#3
[IMG]http://i1100.photobucket.com/albums/g406/tyronet2000/Cresswell%20ND/resize_K5_1580.jpg[/IMG]

#4
[IMG]http://i1100.photobucket.com/albums/g406/tyronet2000/Cresswell%20ND/resize_K5_1584.jpg[/IMG]

Nowt wrong with that Stan. Its definitely variable

I'll get my coat :arrow:

@ tyronet/ Stan

Unfortunately, those dark bands are a feature of this type of variable ND filter. The wider the angle lens, the worse the banding. It means that widening the lens angle means that the amount of 'stopping' you can do reduces.

I have a 67mm one from 7dayshop and nearly sent it back because of this, until I discovered this was a feature.

Below is a table I found somewhere showing the limitations;
12mm: ND4 to ND8 3 stop operating range
15mm: ND4 to ND16 4 stop operating range 

18mm: ND4 to ND32 5 stop operating range

24mm: ND4 to ND64 6 stop operating range

35mm: ND4 to ND125 7 stop operating range

40mm: ND4 to ND175 7.5 stop operating range
50mm: ND4 to ND250 8 stop operating range
70mm: ND4 to ND350 8.5 stop operating range
100mm: ND4 to ND500 9 stop operating range

Hope that helps

Andy

Thanks Andy. I have the 62mm which I had a little more success with. If the thing was calibrated or I had the patience to figure it out it might have helped. I'd bought this because of the high stops. I have some Cokin P types 2,4,8 but the 77mm filter holder only takes one filter to avoid vingetting. Next project try a bit of welding glass as seen used by one of the members. Oh and a day when it isn't raining

Stan, the banding your images exhibit are caused by turning the variable ND filter too far to the maximum setting. Tweak it back a little and these bands will disappear. I know that many will say 'what's the use if you can't set them at maximum', but to be fair these filters are not expensive and to get the same darkening effect with a single filter you would have to buy a strong one and costs therefore get higher. The beauty of the variables is that you can adjust from a mild setting to cutting out a fair amount of light without any banding occurring. I've also had success with mine by using in tandem with a circular polariser - this cuts out much more light without any banding and has enabled me to get 10 second exposures on bright sunny days. They are never going to compete with a Lee Big Stopper and I don't think anyone would expect them to.

Regards
David

I've seen the Big Stopper advertised David, fantastic prices and I believe there is up to a 12 month waiting list for them too.
I think its like everything in photography, practice and get advice. I have the 62mm from 7dayshop and to be honest didn't have a clue when I first got it but had a little success eventually. I need to keep a record of what I set it to, and then try and repeat it. Then I'll give the 77mm a try again.
When using in tandem with a CPL do you have them on the lens then focus through the clearest setting in AF then switch to manual and adjust the filters and shutter speed etc. Thanks for the help

Hi Stan, the best way of focussing I have found is to use Live View. Even with little or no light, Live View presents a pretty good image and enables accurate focussing (BTW, this even works with an Infra-red filter attached which cuts out even more light). With regard to the filter and shutter speed adjustments, I take several test shots and once happy with the exposure I leave it as is. The histogram is vital for this as it is very easy to overexpose the relatively brighter areas if you are not careful.

Regards
David

Thanks to this thread, I think I will have to invest on the ND filter I saw on Amazon.

And publish your results and what you did I hope

Thanks David. I'll have to get down to the seaside again and have a play. Watch this space for some stunning images (in my dreams) I have an IR filter somewhere too but thought I'd read they didn't work well on modern cameras (K7 K5 etc). I know some members have had an *ist modified for IR. I'm probably only remembering half the story though. I'll take the IR filter with me on my next trip. And spare batteries as I'm told live view can use them up quickly
Thank goodness for digital, on my K7 shutter count is 3692, how much would that have cost in film.

Taken with K7 this morning using a Hoya R721 filter and tweaked in photoshop.

K7 18-55mm (kit)f/6.3 1.6sec ISO-800 +0.7 FL38mm

[IMG]http://i1100.photobucket.com/albums/g406/tyronet2000/processed-small-IR_K7_2453.jpg[/IMG]